Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite -axis oriented films grown on thin epitaxial electrodes. The film thickness ranges from 480 down to (seven unit cells). The evolution of the film tetragonality , studied using high resolution x-ray diffraction measurements, shows first a decrease of with decreasing film thickness followed by a recovery of at small thicknesses. This recovery is accompanied by a change from a monodomain to a polydomain configuration of the polarization, as directly demonstrated by piezoresponse atomic force microscopy measurements.
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We note that the polarization direction observed here is opposite to the polarization direction found in the monodomain films grown on (Ref. 8).
